Spotted fever group rickettsia in ticks infesting humans, wild and domesticated animals of Sri Lanka: one health approach

Abstract

Spotted fever group rickettsial infections are considered an emerging infectious disease in Sri Lanka. The present study examined the potential role of tick vectors carrying the infection from sylvatic reservoirs to humans via domesticated animals. Ticks infesting humans, dogs and wild animals were collected island-wide and were identified. Presence of spotted fever group rickettsia in the tick blood meal was determined using PCR in a sub-sample of ticks collected. A total of 30,933 ticks were collected from 30 different hosts and free living stages from the ground.  The collection consisted of 25 tick species recording 12 species from humans, 19 from domesticated animals and 22 from wild animals. Of the total collection randomly selected a sub-sample of 80 ticks were used to identify rickettsia pathogens. This comprised of  fifty ticks from 50 wild animals  belonged to 15 species (wild boar, pangolin, porcupine, barking deer, star tortoise, mouse deer, samber, spotted deer, monkey, civet cat, bandicoot, elephant, fishing cat, rabbit, flying squirrel; and 20 ticks from 15 dogs especially from areas where spotted fever cases were reported and 10 ticks from 10  humans. Results showed that rickettsial infections were found in four tick species, Amblyomma testudinarium collected from a wild boar, Riphicephalus sanguineus from a dog, Amblyomma clypeolatum from a star tortoise and Amblyomma javanense from a pangolin.  Except for A. javanense, other three tick species are generalists infesting humans as well as domestic and wild animals. There is a high potential that these infections can spread easily to humans via the domesticated animals. This is the first report of ticks infesting domesticated and wild animals carrying spotted fever rikettsia and it underscores the possibility of spread of infection from wild reservoirs to human in the animal/human health interface.